Alnus glutinosa L. Gaertn. as potential tree for brackish and saline habitats

Abstract

Over 800 million hectares of land worldwide are affected by salinity. Predicted scenarios of global climate change include a rise in sea level, which may severely affect coastal forest areas. Black alder (Alnus glutinosa) is a tree species known to tolerate heavily waterlogged soils, but its salt resistance is still unclear. The aim of our study was to assess A. glutinosa growth under soil salinity as a possible tree for wet, salt-affected sites in a changing coastal environment due to climate change. We hypothesised that: a) growth parameters are directly related to soil conditions; and b) salinity and waterlogging can limit black alder growth. For our research, we evaluated 9-11-year-old black alder plantations in Poland, one in a saline area and two reference sites on non-saline soils (one with higher moisture content). The growth of trees at each site was characterised by calculating the growth success, mean diameter at breast height, the mean height and the standard deviations from the means. We also calculated the distribution of diameters in each population, regression models for growth as the relationship between diameter and height, and coefficients of variance. The means between sites were compared by one-way ANOVA with Scheffe’s post-hoc comparisons. To characterise soil conditions we took soil samples for each site and compared their properties by the same statistical tests.Under saline conditions, black alder growth was limited in terms of height, diameter at breast height and growth success. Salinity also affected the trees’ variability, growth form and growth pattern. However, these effects were comparable to those observed in the non-saline waterlogged site. The models of growth described by regression demonstrated similar reduction of growth dynamics in these two sites. Moreover, the coefficients of variation in diameter and height of trees in these sites were similar and higher than in non-stressed site. In addition, at the saline and waterlogged sites black alder trees had relatively large number of root suckers, whereas in non-stressed site this was not the case. On the plantations in stressed environments there had been losses in the A. glutinosa stand, which had been spontaneously settled by other species of trees and shrubs, which increased species richness. Therefore, regarding climate change, in our opinion black alder can be considered as an option for planting in brackish coastal areas, where nature conservation and watershed management are at least as important as wood production.